the Rs should be quite a bit louder than the JLs but the JLs will have better SQ. both cases in 9/10 installs. the JLs are most likely a better build but the Rs are definetly better bang for your buck. but if you have the cash the JLs will make a great lil system. personally i like JL, id probably go with them. unless i was trying to be louder id definetly get the Rs: much more SPL potential.
i am a big JL fan and would normally recommend them but if you want loudness then 2 12" alpine R's are gonna be louder then 2 10 JLs. liek trevor said the JL's will have better SQ but w/out a question the 12's will be louder. the price isn't that different you can't tell me that 2 alpine R's 12" cost 150 which is about what JL's cost for 1 off ebay.